JPS6314130B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a construction method for creating a drainage layer (crushed stone pile) using columnar crushed stones underground.

Liquefaction is a phenomenon in which the pore water pressure in the ground increases due to vibrations caused by an earthquake, and the strength of the ground decreases.

As a method to prevent damage caused by this liquefaction, the crushed stone pile method is a construction method that improves the permeability of the ground by creating a drainage layer made of crushed stone underground, and stabilizes the excess pore water pressure generated underground. be.

The sand compaction method has been adopted as a typical construction method, but the problem has been that it has a large effect on vibrations in the surrounding area.

Therefore, for example, when constructing a new tank in close proximity to an existing heavy oil tank, this method could not be adopted because the effect on the existing tank would be extremely large and would be dangerous.

The present invention has been made to improve these drawbacks, and is a crushed stone that has less lateral underground propagation of vibration and can be constructed even in locations close to important facilities such as heavy oil tanks and railway lines. The purpose is to provide a pile construction method.

Next, the construction order of the present invention will be explained.

<1> Setting and driving the casing (first
Figure) Casing 1, which is a hollow circular steel tube, is installed vertically at the pile driving position.

The casing 1 is driven into the ground by the Benoto method or other known method.

This driving should be done slowly so as not to disturb the surrounding ground.

<2> Removing earth from inside the casing (Fig. 2) At the same time as driving the casing 1, or after driving is completed, excavate with the earth auger 2 to discharge the earth and sand inside the casing 1.

<3> Insertion of bottom-filling crushed stones (Fig. 3) After the discharge of the earth and sand in the casing 1 is completed, the bottom-filling crushed stones 4 are introduced into the bottom of the hollow portion 3.

This crushed stone will be constructed to be heavy and thick enough to prevent boiling.

If crushed stone is packed in a bag in advance, casing 1
It is easy to put it inside.

<4> Setting the thin tube (FIG. 4) A hollow steel thin tube 5 is vertically installed in the hollow portion 3 of the casing 1.

The lower end of the thin tube 5 is located on the upper surface of the bottom filling crushed stone 4, and the upper end of the thin tube 5 is located near the upper end of the casing 1.

<5> Filling the casing (Fig. 5) Filling crushed stone 6 is put into the outside of the thin tube 5 in the hollow part 3 of the casing 1, and is filled up to the ground level of the casing 1.

In this case as well, the work will be more efficient if the appropriate amount of crushed stone 6 is packed in bags in advance and lowered into the hollow part 3 using a crane or the like.

<6> Pulling out the casing (Figure 6) Apply force to the casing 1 using a known device such as a benoto and slowly pull it out.

At this time, if a pressure water hose 7 is connected to the upper end of the thin tube 5 and pressure water is supplied, the interlocking of the crushed stones 6 is loosened, and it is possible to prevent the crushed stones from coming up together due to the pulling out of the casing 1.

If the casing 1 is completely pulled out, a pillar of crushed stone will be formed underground.

<7> Vibration by vibrator and drawing of thin tube A known rod-shaped vibrator 8 is suspended and lowered into the thin tube 5.

Then, while applying vibration by the vibrator 8, pull up the thin tube 5, and then pull up the vibrator 8 with a slight delay (Fig. 7). At this time, the lower end of the vibrator 8 is exposed from the lower end of the thin tube 5, and the upper end of the vibrator 8 is inside the thin tube 5. Being located is important. By slowly pulling up the thin tube 5 and the vibrator 8 with the tip of the vibrator 8 exposed, the packed crushed stone 6 is sufficiently compacted at each depth.

When the surface sinks, replenish crushed stone by the amount that has sunk (Figure 8).Finally, when the tube 5 and vibrator 8 are completely pulled up, each depth is sufficiently compacted.
A strong crushed stone pile is completed as a whole. (Fig. 9) As described above, the present invention is a construction method in which a thin tube is inserted into crushed stone, the lower end of the vibrator is exposed, for example, about 2 m from the lower end of the thin tube, and the upper end of the vibrator is always raised while being located within the thin tube. .

As a result, the following effects can be expected.

<B> The excitation position of the vibrator gradually rises.

Therefore, it is possible to compact the crushed stones at each position, and finally it is possible to form a strong pile in which the crushed stones at each depth are sufficiently compacted.

<B> Because the compaction can be done carefully and sufficiently at each depth position, vibrations with a smaller excitation force are sufficient compared to conventional construction methods.

As a result, the propagation of vibration to the surrounding area is extremely low compared to conventional construction methods, and the impact on surrounding structures is small, making it possible to safely perform work on sites close to hydraulic tanks or railway lines, for example. can.

<C> FIG. 10 shows the relationship between acceleration level and distance in the conventional sand compaction method S' and the crushed stone pile method S of the present invention.

Conventional method Vibrohammer KHz12000 type Sand pile φ700, = 13m Present invention method Byrotsu KSV 3000 type Crushed stone pile φ1000, = 10m From this comparison, it can be seen that if the method of the present invention is adopted, the acceleration level can be reduced by about 20 dB at the same point. Recognize.

[Brief explanation of the drawing]

Figures 1 to 9: Explanatory drawings showing the construction order of the present invention; Figure 10: Comparison graph of acceleration levels between the present construction method and the conventional construction method. 1: Casing, 5: Tube, 6: Filled crushed stone,
8: Vibrator.

Claims (1)

[Scope of Claims] 1. A casing is installed in the ground, earth and sand inside the casing is removed to form a hollow part, a thin tube is installed in the hollow part, and the outside of the thin tube in the hollow part of the casing is filled with crushed stone. , a crushed stone pile construction method characterized by pulling out the casing, suspending it inside the narrow tube, and lifting the narrow tube and vibrator while applying vibration to the packed crushed stone using a vibrator whose lower end is exposed in the crushed stone from the lower end of the narrow tube. .